with small fenestrae, morphologically quite dis-
tinct from the large honeycomb-patterned
fenestrae in Chytridiales, was recently observed
in zoospores ofAlogomyces(Simmons et al.
2012 ). Zoospores contain a ribosomal aggrega-
tion around the nucleus and one to several
lipid globules in the MLC. No organized micro-
tubule root has been observed in any of the
zoospores.
- Polychytriales
The Polychytriales (Longcore and Simmons
2012 ) was erected based on thePolychytrium
clade (James et al.2006b). Its members are
rhizophlyctoid chytrids (Dogma 1973 )in
which rhizoids emanate from multiple sites on
the sporangium. All members grow on chitin,
and all exceptKarlingiomyces asterocystisare
able to grow on cellulose and keratin. The order
consists of five genera (Arkaya,Karlingiomyces,
Lacustromyces, Neokarlingia, Polychytrium),
two of which are newly described and include
new combinations with existing species:
ArkayawithRhizophlyctis serpentinaandNeo-
karlingiawithRhizophlyctis (Karlingia) chiti-
nophila. Three of the genera are monocentric,
and two genera,PolychytriumandLacustro-
myces, are polycentric with broadly tubular rhi-
zomyceliums (Fig.6.2N)lacking the turbinate
swellingscharacteristic of polycentric members
of the Cladochytriales. The only operculate
genus is Karlingiomyces (Blackwell et al.
2004 ); the other genera release zoospores
through inoperculate openings. Polychytriales
is the sister group of Cladochytriales (James
et al.2006b), a clade that also includes mono-
centric and polycentric thalli but is character-
ized by growth on cellulose rather than chitin.
Each genus has a distinct suite of zoospore
ultrastructural characters. The zoospore ultra-
structure (Fig.6.5E) is remarkably varied in this
order (Longcore 1993 ; Longcore and Simmons
2012 ) and harkens diversity that is likely to be
discovered. The zoospores are spherical and
relatively large, typically greater than 4mmin
diameter. The zoospores are distinctive because
the nonflagellated centriole is longer than that
in other orders, with its length equal to or
exceeding its diameter and with copious
densely packaged fibrillar material joining the
kinetosome the full length of the nonflagellated
centriole. Microtubule roots range from three
to none, and an electron-opaque plug in the
transition region of the flagellum occurs in
three of the five genera.Lacustromyceshas the
most extensive microtubule root system with
three roots, one of which is massive and embed-
ded in dense material (Longcore 1993 ). The
MLC is varied and includes multiple lipid glo-
bules surrounded by or embedded in an exten-
sive microbody in Polychytrium aggregatum
andLacustromyces hiemalis. The MLC cisterna
is fenestrated only in zoospores ofArkaya, and
the MLC cisterna is reported to be absent in the
other genera.- Spizellomycetales
The earliest chytrids described were aquatic
parasites of algae and were discovered by bota-
nists observing algae (Braun 1851 , 1855 ). Barr
( 1980 ) and Longcore et al. ( 1995 ) recognized that
zoospores of more recently described soil-
inhabiting species of two historic genera,Phlyc-
tochytriumandEntophlyctis, were different from
zoospores of the type species of these genera,
which were algal parasites. Consequently, new
genera were erected for soil-inhabiting species of
PhlyctochytriumandEntophlyctisand were clas-
sified in a newly established order, Spizellomy-
cetales (Barr 1980 ,1984b;Longcoreetal. 1995 ).
Spizellomycetales was the first order separated
from Chytridiales based on fundamental differ-
ences in zoospore ultrastructure (Barr 1980 ).
Members of Spizellomycetales are distinct from
other chytrids because they lack the translation
elongation factor 1-alpha gene (EF-1 alpha) and
instead possess the paralog,elongation factor-
like gene(EFL) (James et al.2006a; Keeling and
Inagaki 2004 ; Simmons 2011 ; Simmons and
Longcore 2012 ). Whether or not the paralog
EFL is due to lateral gene transfer or to gene
duplication and loss (Keeling and Inagaki
2004 ), its presence in all Spizellomycetales
examined so far suggests a single evolutionary
event corresponding to a major radiation of a
chytrid lineage in soil.Chytridiomycota, Monoblepharidomycota, and Neocallimastigomycota 159